The TV I had got updates for ARC, frame gen, brightness adjustment, etc.
Your statement is false. There are reasons to update.
FWIW, I'd bet you'd never have noticed the difference.
You've got to be careful, though. Consider that they have non-deletable apps, tiny amounts of onboard storage, and that every "app" WILL bloat over time. So, with those updates installing the latest version of Netflix, Prime, HBO Max, Paramount, Tubi, LG Channels™ etc... it means it's filling your 4GB or whatever storage fuller and fuller. Eventually the storage will be nearly full, which shouldn't matter, except that it's a computer, and having storage nearly full makes it slow as shit to do everything, even "boot up" and "change inputs".
The TV I had got updates for new ads and reduced speed
Exactly this. I've had ones for 10+ years that were never connected to the internet and they functioned perfectly well as dumb TVs.